The present invention relates to the process measurement and control industry. More specifically, the present invention relates to magnetic flowmeters of the type used to measure flow of a process fluid.
Magnetic flow meters are used to measure flow of a conductive process fluid through a flowtube. The conductive fluid flows past an electromagnet and electrodes. In accordance with Faraday's law of electromagnetic induction, an electromotive force (EMF) is induced in the fluid due to an applied magnetic field. The EMF is proportional to the flow velocity of the fluid. The electrodes are positioned in the flowtube to make electrical contact with the flowing fluid. The electrodes sense the EMF that is magnetically induced in the fluid which can then be used to determine flow rate. The EMF is measured by the flow meter using a differential front end amplifier connected across the electrodes. The potential of the process fluid is used as a reference for the differential amplifier.
In some industrial installations, the calibration of the flowmeter must be verified to be within certain limits, for example a percent of required accuracy. Various techniques are used to verify flowmeter operation. These include shutting down the process, removing the flowtube from the process and sending the flowtube to an off site location to verify calibration. The off site location may be, for example, a factory, a certified lab or an in house location where tests are performed using additional equipment such as a “prover” or a reference meter. In some configurations, an external device can be used that is connected to the flowtube and the transmitter. This external device then verifies that the original characteristics of the flowtube and transmitter have not changed significantly. These procedures are expensive, cumbersome and require a trained technician to perform the testing.